Defocused laser drilling process for forming a support member of a fabric forming device

ABSTRACT

Method of forming a topographical support member for use in producing nonwoven fabrics such as tricot nonwoven fabrics is accomplished by focusing a laser beam so that the focal point is below the top surface of a starting workpiece. The laser beam is used to drill a predetermined pattern of tapered apertures. The pattern of tapered apertures forms the cluster of peaks and valleys surrounding each aperture on the top surface of the resulting support member.

RELATED APPLICATIONS

This application is a continuation-in-part of commonly assigned U.S.application Ser. No. 131,191, filed Sep. 13, 1993, now abandoned.

BACKGROUND OF THE INVENTION

Nonwoven fabrics have been known for many years. In one process forproducing nonwoven fabrics, a fiber batt or web is treated with waterstreams to cause the fibers to entangle with each other and provide somestrength in the batt. Many methods have been developed for treatingfiber batts in this manner in an attempt to duplicate the physicalproperties and appearance of woven fabrics.

U.S. Pat. Nos. 5,098,764 and 5,244,711 disclose backing members forsupporting a fibrous web during the manufacture of nonwoven fabrics. Thesupport members disclosed in U.S. Pat. No. 5,098,764 have apredetermined topography as well as a predetermined pattern of openingswithin that topography. In one specific embodiment, the backing memberis three-dimensional and includes a plurality of pyramids disposed in apattern over one surface of the backing member. This specific backingmember further includes a plurality of openings which are disposed inthe spaces, referred to as "valleys", between the aforementionedpyramids. In this process, a starting web of fiber is positioned on thetopographical support member. The support member with the fibrous webthereon is passed under jets of high pressure fluid, typically water.The jets of water cause the fiber to intertwine and interentangle witheach other in a particular pattern, based on the topographicalconfiguration of the support member.

The pattern of topographical features and apertures in the supportmember is critical to the structure of the resulting nonwoven fabric. Inaddition, the support member must have sufficient structural integrityand strength to support a fibrous web while fluid jets rearrange thefibers and entangle them in their new arrangement to provide a stablefabric. The support member must not under go any substantial distortionunder the force of the fluid jets. Also, the support member must havemeans for removing the relatively large volumes of entangling fluid soas to prevent "flooding" of the fibrous web, which would interfere witheffective entangling. Typically, the support member includes drainageapertures which must be of a sufficiently small size to maintain theintegrity of the fibrous web and prevent the loss of fiber through theforming surface. In addition, the support member should be substantiallyfree of burrs, hooks or the like irregularities that could interferewith the removal therefrom of the entangled fabric. At the same time,the support member must be such that fibers of the fibrous web beingprocessed thereon are not washed away under the influence of the fluidjets.

While machining may be used to fabricate such topographical supportmembers, such a method of manufacture is extremely expensive and oftenresults in aforementioned burrs, hooks and irregularities. Thus, thereis a need for a method for making topographical support members whichmethod is less expensive and reduces the numbers of burrs, hooks andirregularities therein.

SUMMARY OF THE INVENTION

The present invention is directed to a method of forming a topographicalsupport member for producing nonwoven fabrics and to the topographicalsupport member formed by the method of the invention which can be usedto produce tricot-like or other similar nonwoven fabrics. In accordancewith the method of the present invention, a laser beam is directed ontoa workpiece to be engraved with a topographical pattern. The laser beamis focused such that the focal point of the beam is below the topsurface of the workpiece. The focusing of the laser beam at a pointother than the top surface of the workpiece, e.g. at a point below thetop surface, instead of on the surface is termed "defocusing."Thereafter, the defocused laser beam is used to drill a predeterminedpattern of tapered apertures in the workpiece in such a manner to form atopographical array of peaks and valleys surrounding each aperture ofthe workpiece. The apertures have a tapered or conical-like top portionangled such that the major diameter of the aperture resides on the topsurface of the resulting support member. The topographical array ofpeaks and valleys is formed by the center line to center line spacing ofadjacent apertures being less than the major diameter of the top portionof the apertures. Such a spacing results in the taper of adjacentapertures intersecting within the starting thickness of the workpiece.

In one embodiment, a raster scan laser drilling process is used to formthe topographical support member. In this embodiment, the laser beam ismoved in a series of raster scans over the surface of the workpiece.During each scan, the laser is turned on at predetermined intervals ofsufficient time and intensity to drill one or more discrete portions ofeach of the apertures. In this method, each aperture will take amultiplicity of scans to be drilled in its entirety. In one embodiment,the pattern of the plurality of peaks, valleys and apertures isconfigured to produce a nonwoven fabric having the appearance of atricot knit fabric.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one type of topographical support memberof the present invention.

FIG. 2 is a cross-sectional view taken along lines 2--2 of FIG. 1.

FIG. 3 is a bit map of the laser instructions defining a pattern ofapertures to be drilled in a workpiece to form the topographical supportmember of FIG. 1.

FIG. 4 is a diagrammatic view of an apparatus for forming atopographical support member of the present invention.

FIG. 5 depicts the smallest rectangular repeat element, 25 pixels longand 15 pixels wide, of the pattern shown in FIG. 3.

FIG. 6 is a block diagram showing the various steps of the process ofproducing nonwoven fabrics using a support member of the presentinvention.

FIG. 7 is a schematic sectional view of one type of apparatus forproducing nonwoven fabrics using a support member of the presentinvention.

FIG. 8 is a diagrammatic view of another type of apparatus for producingnonwoven fabrics using a support member of the present invention.

FIG. 9 is a diagrammatic view of a preferred type of apparatus forproducing nonwoven fabrics using a support member of the presentinvention.

FIG. 10 is a photomicrograph of a tricot-like nonwoven fabric, enlargedabout 20 times, as seen from its upper surface, formed using thetopographical support member of FIG. 1.

FIG. 11 is a photomicrograph of the tricot-like nonwoven fabric of FIG.9 as seen from its bottom surface.

FIG. 12 is a bit map, similar to that depicted in FIG. 3, of a differentset of laser instructions.

FIG. 13 is a digitized image of a support member of the presentinvention from a scanning electron microscope.

FIG. 14 is another digitized image of the support member shown in FIG.13.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, a topographical support member of thepresent invention is shown in perspective in FIG. 1.

The support member 2 comprises a body 1 having a top surface 3 andbottom surface 4. Disposed in a predetermined pattern across top surface3 is an array of peaks 5 separated by valleys 6. A plurality of drainageapertures 7 extending through the thickness of the support member aredisposed in a pattern in the member 2. In this embodiment, each drainageaperture 7 is surrounded by a cluster of six peaks 5 and six valleys 6.

Drainage aperture 7 comprises an upper portion 7a and a lower portion7b. As can be seen in FIG. 1, upper portion 7a of aperture 7 comprises awall 10 and is generally "bell-mouthed" or "flared" in configuration.Upper portion 7a is tapered, having a cross-sectional area which islarger nearer the top surface of support member 2 and a cross-sectionalarea which is smaller at the point 10a where the bottom of said upperportion meets the top of lower portion 7b. Lower portion 7b, in thespecific embodiment under discussion, has a somewhat tapered cylindricalconfiguration. The cross-sectional area of lower portion 7b of aperture7 is greater at point 10a then at the bottom surface 4 of the supportmember. An aperture 7 is shown in cross-section in FIG. 2. Lines 9 aredrawn tangent to opposed points on walls 10 one hole radius below topsurface 3. The angle 11 formed by lines 9 must be controlled relative tothe thickness 12 of the support member 2 to produce the intended result.For example, if the angle is too great, the aperture will be too smalland therefore insufficient drainage will be provided. If the angle istoo small, there will be very few or no peaks and valleys.

The center-to-center spacing, S, of adjacent apertures (See FIG. 1) inthe repeating pattern is of similar importance. The peaks 5 and valleys6 are created by the intersection of the tapered somewhat conicalapertures 7. If the center-to-center spacing of the apertures weregreater than the major diameter of aperture 7 at the top surface 3, nointersection would result, and the member would be a smooth, flat topsurface with conical apertures disposed throughout. Referring to FIG.13, the major diameter of aperture A' extends between peaks 501 and 504and is identified by double-headed arrow 521. Similarly, the majordiameter of aperture B' extends between peaks 503 and 512 and isidentified by double-headed arrow 522. The major diameter of a givenaperture is the largest peak-to-peak distance, measured at the topsurface of the support member, between any pair of peaks defining theupper portion of the aperture. When the center-to-center spacing ofadjacent apertures is less than the aperture diameters measured alongthat center-to-center line, the conical surfaces intersect forming avalley.

Referring now to FIG. 3, apertures 7 are depicted as hexagons in anested array, but the invention is not limited to hexagons. Othershapes, such as for example circles, squares, octagons, or irregularshapes (See FIG. 12), or combinations thereof, may be used, depending onthe desired topographical configuration. Rows 13 and 14, runningparallel to directional arrow A in FIG. 3, each comprise a plurality ofhexagons 150. These hexagons are 7 pixels wide, 11 pixels long andwithin each row are spaced 8 pixels apart. Row 13 of hexagons is spacedclosely to row 14 of hexagons. Specifically, as can be seen in FIG. 3,the lower tip of each hexagon in row 13 is tangent to line 17, whichline 17 is also tangent to the upper tip of each hexagon in row 14. Rows15 and 16 duplicate the pattern and spacing of rows 13 and 14. Thespacing between rows 15 and 16 corresponds substantially to theabove-mentioned spacing between rows 13 and 14. Row 15, however, isspaced from row 14. As seen in FIG. 3, the lowermost tips of thehexagons in row 14 are tangent to line 18, while the uppermost tips ofthe hexagons in row 15 are tangent to line 19. Lines 18 and 19 arespaced from each other by a distance, d, which in the patternillustrated in FIG. 3, is 3 pixels. The above-described pattern of therows 13, 14, 15 and 16 is repeated throughout the bit map of FIG. 3. Itwill be understood that the spacing of the hexagons may be non-uniformwithin a given row or between adjacent rows.

The distance between parallel adjacent walls 20 of two adjacent hexagonsshown in the bit map of FIG. 3 must be sufficient to give the supportmember strength to resist the fluid forces and allow normal handling.

Referring to FIG. 1, each aperture 7 is surrounded by six adjacentapertures 7. If all of these apertures 7 have sufficient taper to creatediameters greater than their respective center-to-center spacing, eachaperture 7 will have six intersections with its neighbors, and theseintersections will produce six valleys 6.

Depending on their depth, these valleys 6 can either intersect the topsurface 3, resulting in their being separated by small plateaus, or theycan intersect each other and produce a peak 5.

The apparatus of the present invention used to produce topographicalsupport members is shown in FIG. 4. The starting material for thesupport member may be any desired shape or composition. Thetopographical support member preferably comprises acetal; acrylic willalso perform satisfactorily. In addition, the preferred shape of thestarting material is a thin wall, cylindrical, preferably seamless, tubethat has been relieved of residual internal stresses. As will bedescribed later, the cylindrical shape accommodates the preferredapparatus for producing the nonwoven fabrics.

Tubes manufactured to date for use in forming support members are 2 to 6feet in diameter and have a length ranging from 2 to 16 feet. The wallthickness is nominally 1/4 inch. These sizes are a matter of designchoice.

A starting blank tubular workpiece is mounted on an appropriate arbor,or mandrel 21 that fixes it in a cylindrical shape and allows rotationabout its longitudinal axis in bearings 22. A rotational drive 23 isprovided to rotate mandrel 21 at a controlled rate. Rotational pulsegenerator 24 is connected to and monitors rotation of mandrel 21 so thatits precise radial position is known at all times.

Parallel to and mounted outside the swing of mandrel 21 is one or moreguide ways 25 that allow carriage 26 to traverse the entire length ofmandrel 21 while maintaining a constant clearance to the top surface 3of tube 2. Carriage drive 33 moves the carriage along guide ways 25,while carriage pulse generator 34 notes the lateral position of thecarriage with respect to support member 2. Mounted on the carriage isfocusing stage 27. Focusing stage 27 is mounted in focus guide ways 28and allows motion orthogonal to that of carriage 26 and provides a meansof focusing lens 29 relative to top surface 3. Focus drive 32 isprovided to position the focusing stage 27 and provide the focusing oflens 29.

Secured to focusing stage 27 is the lens 29, which is secured in nozzle30. Nozzle 30 has means 31 for introducing a pressurized gas into nozzle30 for cooling and maintaining cleanliness of lens 29.

Also mounted on the carriage 26 is final bending mirror 35, whichdirects the laser beam 36 to the focusing lens 29. Remotely located isthe laser 37, with optional beam bending mirrors 38 to direct the beamto final beam bending mirror 35. While it would be possible to mount thelaser 37 directly on carriage 26 and eliminate the beam bending mirrors,space limitations and utility connections to the laser make remotemounting far preferable.

When the laser 37 is powered, the beam 36 emitted is reflected first offbeam bending mirror 38, then final beam bending mirror 35, which directsit to lens 29. The path of laser beam 36 is configured such that, iflens 29 were removed, the beam would pass through the longitudinalcenter line of mandrel 21.

With lens 29 in position, the beam is focused below, but near the topsurface 3. Focusing the beam below the top surface is identified as"defocusing" the laser beam relative to the surface of the tube.

While this invention could be used with a variety of lasers, thepreferred laser is a fast flow CO₂ laser, capable of producing a beamrated at up to 2500 watts. This process is in no way dependent on such ahigh power laser, as support surfaces have been successfully drilledwith a slow flow CO₂ laser rated at 50 watts.

When focusing lens 29 passes beam 36, it concentrates the energy nearthe center of the beam. The rays are not bent through a single point,but rather a spot of small diameter. The point of smallest diameter issaid to be the focus or focal point. This occurs at a distance from thelens said to be the focal length. At lengths either shorter or greaterthan the focal length, measured spot sizes will be greater than theminimum.

The sensitivity to focus position is inversely proportional to focallength. Minimum spot size is directly proportional to focal length.Therefore, a short focal length lens can achieve a smaller spot size butmust be more accurately positioned and is affected dramatically bysurface run-out. Longer focal length lenses are more forgiving of targetpositioning, but can only achieve somewhat larger spot sizes. Thus, inaddition to the power distribution contributing to the tapered topportion of the drilled aperture, the defocusing of the beam below thesurface also contributes to the angle and length of the taper, and hencethe shape and size of the peaks and valleys.

In order to fabricate a support member, an initial focusing step must beperformed. Once a blank tubular workpiece 2 is positioned on the mandrel21, the laser is pulsed briefly and the mandrel rotated slightly betweenpulses such that a series of small depressions is produced. The focusstage 27 is then moved with respect to the mandrel center line to changethe focus position and another series of depressions is produced.Typically a matrix of 20 rows of 20 depressions each is drilled. Thedepressions are examined microscopically, and the column of smallestdepressions identified. This is established as the reference diameterfor top surface 3 of the blank tubular workpiece at which the beam wasfocused.

A desired pattern is selected, such as the one shown in FIG. 3. Thepattern is examined to determine the number of repeats that will berequired to cover the circumference of the workpiece and complete thesurface without an obvious seam. Similarly, the advance along thelongitudinal axis of the tubular workpiece per repeat and total numberof repeats is established. These data are entered into a computercontrol for operating the laser drilling machine.

In operation, the mandrel, with the tubular workpiece mounted thereon,is rotated in front of the lens. The carriage is motored so that thefirst aperture position corresponds with the focal point of the lens 29.The focus stage is motored inward, placing the focal point inside theinterior of the material to be drilled. The laser is then pulsed, withsome combination of pulse power level and duration. As seen in FIG. 2,the diameter of the aperture at the top surface 3 is considerably largerthan the diameter of the aperture at the lower surface 4. In order toachieve the desired topographical configuration, two factors need to bemeasured and controlled. First, the degree with which the lens isfocused into the interior of the workpiece increases the cone angle 11,and second, increasing the power level or pulse duration increases thedepth and diameter. Once an aperture of the proper diameter and taper isachieved, the rotational drive and carriage drive can be indexed toreposition the support member such that the next intended hole positioncorresponds to the focal point. The process is then repeated until theentire pattern has been drilled. This technique is known as "percussion"drilling.

If the laser selected is of sufficient power, the mandrel and carriagedo not need to be stopped during the laser pulse. The pulse can be ofsuch short duration that any movement of the workpiece during thedrilling process is inconsequential. This is known in the trade as"fire-on-the-fly" drilling.

If the laser can recover rapidly enough, the workpiece can be rotated ata fixed speed and the laser pulsed once to create each hole. In apattern such as the one shown in FIG. 3, the laser would normally bepulsed to produce a complete column, the carriage indexed to the nextcolumn position and the beam pulsed for the next series of apertures.

One problem that may occur depending on the type of material and densityof the pattern of apertures, is the introduction of a large amount ofheat into a small area of the forming surface. Gross distortion, and theloss of pattern registration may result. Under some conditions, majordimensional changes of the part results, and the surface is neithercylindrical nor the right size. In extreme cases, the tube may crack.

A preferred embodiment of the present invention, which eliminates thisproblem, uses a process called defocused raster scan drilling.

In this approach, the pattern is reduced to the smallest rectangularrepeat element 41 as depicted in FIG. 5. This repeat element containsall of the information required to produce the pattern in FIG. 3. Whenused like a tile and placed both end-to-end and side-by-side, the largerpattern is the result.

This repeat element is further divided into a grid of smallerrectangular units or "pixels" 42. Though typically square, for somepurposes, it is more convenient to employ pixels of unequal proportions.

Each column of pixels represents one pass of the workpiece past thefocal position of the laser. This column is repeated as many times as isrequired to reach completely around support member 2. Each pixel wherethe laser is intended to create a hole is black. Those pixels where thelaser is turned off are white.

To begin drilling at the top of the first column of pixels in FIG. 5,while the mandrel is turning at a fixed rate, the laser is turned on,maintained at a constant power level for 11 pixels and then switchedoff. These pixels are counted by the rotational pulse generator 24 inFIG. 4. The laser remains off for the next 14 units. This laser off/onsequence is repeated for the first revolution, at which point themandrel is back to starting position, carriage drive 33 has repositionedthe carriage one unit and the computer is ready to do column 43a.

During column number 43a, the laser has a shorter "on time" (now 9units) and longer "off time" (now 16 units). The total number of on andoff times is a constant based on the pattern height.

This process is repeated until all of the columns have been used over anentire revolution each; in the case of FIG. 5, there were 15 revolutionsof the mandrel. At this point, the process returns to the instructionsin column 43.

Note that in this approach, each pass produces a number of narrow cutsin the material, rather than a large hole. Because these cuts areprecisely registered to line up side-by-side and overlap somewhat, thecumulative effect is a hole. In the pattern of FIG. 5, each hexagonalhole 44 actually requires 7 passes separated by a complete revolution,distributing the energy around the tube and minimizing local heating.

If, during this drilling operation, the lens was focused at the topsurface of the material, the result would be hexagonal holes withreasonably parallel walls. The combination of raster scan drilling withthe defocused lens approach, however, produces the forming surface ofFIG. 1.

In the present invention, the apertures 7 are quite small and numerous.Typical patterns range from 800 to 1400 apertures per square inch.

The process to manufacture a nonwoven fabric using a support member ofthe present invention has been described in U.S. Pat. Nos. 5,098,764 and5,244,711, both of which are incorporated by reference herein.

FIG. 6 is a block diagram showing the various steps in the process ofproducing the novel nonwoven fabrics of the present invention. The firststep in this process is to position a web of fibers on a topographicalsupport member (Box 1). The fibrous web is presoaked or wetted out whileon this support member (Box 2) to ensure that as it is being treated itwill remain on the support member. The support member with the fibrousweb thereon is passed under high pressure fluid ejecting nozzles (Box3). The preferred fluid is water. The water is transported away from thesupport member, preferably using a vacuum (Box 4). The fibrous web isde-watered (Box 5). The de-watered formed fabric is removed from thesupport member (Box 6). The formed fabric is passed over a series ofdrying drums to dry the fabric (Box 7). The fabric may then be finishedor otherwise processed as desired (Box 8). FIG. 7 is a schematicrepresentation of one type of apparatus for carrying out the process andproducing the fabrics of the present invention. In this apparatus, aforaminous conveyor belt 70 moves continuously about two spaced apartrotating rolls 71 and 72. The belt is driven so that it can bereciprocated or moved in either a clockwise or counterclockwisedirection. At one position on the belt, in the upper reach 73 of thebelt, there is placed above the belt a suitable water ejecting manifold74. This manifold has a plurality of very fine diameter holes, of about7/1000 of an inch in diameter, with about 30 holes per inch. Water underpressure is driven through these holes. On top of the belt is placed atopographical support member 75 and on top of that topographical memberthe fiber web 76 to be formed is placed. Directly beneath the watermanifold, but under the upper reach of the belt, is a suction manifold77 to aid in removing the water and prevent flooding of the fiber web.Water from the manifold impinges on the fiber web, passes through thetopographical support member and is removed by the suction manifold. Asmay be appreciated, the topographical support member with the fibrousweb thereon may be passed under the manifold a number of times asdesired to produce fabrics in accordance with the present invention.

In FIG. 8 there is depicted an apparatus for continuously producingfabrics in accordance with the present invention. This schematicrepresentation of the apparatus includes a foraminous conveyor belt 80which actually serves as the topographical support member in accordancewith the present invention. The belt is continuously moved in acounterclockwise direction about spaced apart rotating rolls as is wellknown in the art. Disposed above this belt is a fluid feeding manifold79 connecting a plurality of lines or groups 81 of orifices. Each grouphas one or more rows of very fine diameter holes with 30 or more holesper inch. The manifold is equipped with pressure gauges 88 and controlvalves 87 for regulating the fluid pressure in each one or group oforifices. Disposed beneath each orifice line or group is a suctionmember 82 for removing excess water, and to keep the area from flooding.The fiber web 83 to be formed into the nonwoven fabric of the presentinvention is fed onto the topographical support member conveyor belt.Water is sprayed through an appropriate nozzle 84 onto the fibrous webto pre-wet the web and aid in controlling the fibers as they pass underthe pressure manifolds. A suction slot 85 is placed beneath this waternozzle to remove excess water. The fibrous web passes under the fluidfeeding manifold with the manifold preferably having an increasedpressure. For example, the first lines of holes or orifices may supplyfluid forces at 100 psi, while the next lines of orifices may supplyfluid forces at a pressure of 300 psi, and the last lines of orificessupply fluid forces at a pressure of 700 psi. Though six fluid supplyinglines of orifices are shown, the number of lines or rows of orifices isnot critical, but will depend on the weight of the web, the speed ofoperation, the fluid pressures used, the number of rows of holes in eachline, etc. After passing between the fluid feeding and suction manifoldsthe formed fabric is passed over an additional suction slot 86 to removeexcess water from the web.

A preferred apparatus for producing fabrics in accordance with thepresent invention, is schematically depicted in FIG. 9. In thisapparatus, the topographical support member is a rotatable drum 90. Thedrum rotates in a counterclockwise direction. Drum 90 may be acontinuous cylindrical drum or may be made of a plurality of curvedplates 91 disposed so as to form the outer surface of the drum. Ineither case, the outer surface of drum 90 or the outer surfaces of thecurved plates 91 comprise the desired topographical supportconfiguration. Disposed about a portion of the periphery of the drum isa manifold 89 connecting a plurality of orifice strips 92 for applyingwater or other fluid to a fibrous web 93 placed on the outside surfaceof the curved plates. Each orifice strip may comprise one or more rowsof very fine diameter holes of approximately 5/1000 of an inch to10/1000 of an inch in diameter. There may be as many as 50 or 60 holesper inch or more if desired. Water or other fluid is directed throughthe rows of orifices. The pressure in each orifice group is increasedfrom the first group under which the fibrous web passes to the lastgroup. The pressure is controlled by appropriate control valves 97 andmonitored by pressure gauges 98. The drum is connected to a sump 94 onwhich a vacuum may be pulled to aid in removing water and to keep thearea from flooding. In operation, the fibrous web 93 is placed on theupper surface of the topographical support member before the waterejecting manifold 89. The fibrous web passes underneath the orificestrips and is formed into a tricot-like nonwoven fabric. The formedfabric is then passed over a section 95 of the apparatus where there areno orifice strips, but vacuum is continued to be applied. The fabricafter being de-watered is removed from the drum and passed around aseries of dry cans 96 to dry the fabric.

As noted above, the support member shown in FIG. 1 will produce atricot-like nonwoven fabric. FIG. 10 is a copy of a photomicrograph of atricot-like nonwoven fabric at an enlargement of approximately 20 times.The fabric 100 is made from a plurality of fibers. As seen in thephotomicrograph, the fibers are intertwined and interentangled and forma pattern of openings 110 in the fabric. A number of these openingsinclude a loop 120 formed from fiber segments. Each loop is made from aplurality of substantially parallel fiber segments. The loops are in theshape of a U with the closed end of the U pointed upwardly towards theupper surface of the fabric as viewed in the photomicrograph. FIG. 11 isa copy of a photomicrograph of the opposite, i.e. bottom, surface offabric 100 of FIG. 10 at an enlargement of about 20 times. The fibers inthe fabric are intertwined and entangled to form a pattern of openings110 in the fabric. In some of these openings there are U-shaped loops120 formed from substantially parallel fiber segments. When viewed fromthis bottom surface of the fabric, the open end of the U-shaped loop ispointed towards the surface of the fabric viewed in thisphotomicrograph.

EXAMPLE 1

A support member made of acetal with an average thickness of 6 mm wasproduced using the following parameters:

Focus Position=2.5 mm below material surface

Lens Type=Positive Meniscus

Lens Focal Length=5 inches

Laser Power=1300 watts

Surface Speed of Tube on Mandrel=20.3 m/min

Longitudinal Carriage Advance/Rev=0.05 mm

Pixel Size=0.05 mm

FIG. 12 is a pixel by pixel depiction of the on/off laser power patternprogrammed into the computer control. The pattern consisted of repeatingpairs of rows of apertures, labeled A₁, B₁, A₂, B₂, etc. The aperturesin each A row have a first irregular shape and the apertures in each Brow have a second irregular shape. A tubular workpiece approximately 3feet in diameter, 12 feet long and 6 mm thick was laser drilled usingthe apparatus of FIG. 4 operated according to the instructions containedin FIG. 12 to provide the support member shown in FIGS. 13 and 14. Thelaser drilling process took about 7 days to complete.

In FIG. 13, the illustrated support member comprises a first row A ofapertures (seen in the upper part of FIG. 13), a next adjacent row B ofapertures and a second row A of apertures below row B of apertures.First row A of apertures includes aperture A'. Next adjacent row B ofapertures includes aperture B' which is adjacent to aperture A'. Theupper portion of aperture A' is surrounded and defined by peaks 501,502, 503, 504, 505 and 506. The upper portion of aperture B' issurrounded and defined by peaks 510, 511, 512, 513, 504 and 503. It willbe recognized that peaks 504 and 503 are common to both of apertures A'and B'. Line 521 (Double arrowhead) extending between peaks 501 and 504constitutes the major diameter of the upper portion of aperture A', saidmajor diameter being 0.085 inch in the support member being described.Similarly, line 522 extending between peaks 503 and 512 constitutes themajor diameter of the upper portion of aperture B', said major diameterbeing 0.075 inch in the support member being described.

The various peak-to-peak distances associated with aperture A' in thesupport member being discussed are set forth in Table 1. The variouspeak-to-peak distances associated with aperture B' in the support memberare set forth in Table II.

                  TABLE I                                                         ______________________________________                                        (Dimensions in inches)                                                        PEAK No.  501       502    503    504  505                                    ______________________________________                                        501       --        --     --     --   --                                     502       0.037     --     --     --   --                                     503       0.067     0.040  --     --   --                                     504       0.085     0.067  0.037  --   --                                     505       0.070     0.075  0.055  0.035                                                                              --                                     506       0.035     0.056  0.065  0.065                                                                              0.040                                  ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        (Dimensions in inches)                                                        PEAK No.  510       511    512    513  503                                    ______________________________________                                        510       --        --     --     --   --                                     511       0.037     --     --     --   --                                     512       0.062     0.035  --     --   --                                     513       0.065     0.056  0.037  --   --                                     503       0.035     0.066  0.075  0.063                                                                              --                                     504       0.055     0.067  0.055  0.037                                                                              0.037                                  ______________________________________                                    

FIG. 14 is the same digitized image as that shown in FIG. 13 but it hasbeen marked and numbered to show the distance between the bottom of avalley between two adjacent peaks and a line connecting the same twopeaks. For example, line 530 in FIG. 14 connects peaks 503 and 504associated with aperture A'. The depths of the valleys between peaks501-506 associated with aperture A' are shown in the upper portion ofTable III. The depths of the 2 valleys associated with aperture B', i.e.the valleys between peaks 510 and 511 and the valley between peaks 504and 513, are shown in the lower portion of Table III. The valleysbetween the remaining peaks associated with aperture B', those betweenpeaks 511 and 512, and between 512 and 513, are structurally analogousTable III to those valleys between peaks 501 and 506, and 501 and 502respectively.

                  TABLE III                                                       ______________________________________                                        Valley Between Peaks                                                                          Valley Depth Inches                                           ______________________________________                                        501 and 502     0.016                                                         502 and 503     0.020                                                         503 and 504     0.024                                                         504 and 505     0.025                                                         505 and 506     0.020                                                         506 and 501     0.012                                                         510 and 511     0.026                                                         504 and 513     0.026                                                         ______________________________________                                    

While several embodiments and variations of the present invention aredescribed in detail herein, it should be apparent that the disclosureand teachings of the present invention will suggest many alternativedesigns to those skilled in the art.

What is claimed is:
 1. A method for forming a topographical supportmember for producing a nonwoven fabric comprising the steps of:a)providing a workpiece, b) focusing a laser beam such that the focalpoint is below the top surface of said workpiece; and c) drilling withsaid laser beam a plurality of tapered apertures through said workpiece,said plurality of apertures being drilled in a pattern predetermined toform an array of peaks and valleys surrounding each aperture therebyforming a topographical top surface on the resulting support member. 2.The method of claim 1 wherein said drilling step includes pulsing thelaser beam in a predetermined sequence of on and off states.
 3. Themethod of claim 2 wherein the laser beam on states are of sufficienttime and intensity to drill each aperture in a single on pulse.
 4. Themethod of claim 3 wherein the step of moving the laser beam includesrotating said workpiece about its longitudinal axis and indexing thelaser beam along said longitudinal axis after each revolution of theworkpiece.
 5. The method of claim 2 wherein the laser beam on states areof sufficient time and intensity to drill a discrete unit of eachaperture in a single on pulse.
 6. The method of claim 5 furtherincluding the step of moving the laser beam in a series of raster scansover the surface of the workpiece, the laser beam on states being ofsufficient time and intensity to drill one or more discrete units ofsaid apertures in each raster scan.
 7. The method of claim 6 wherein thestep of moving the laser beam includes rotating said workpiece about itslongitudinal axis and indexing the laser beam along said longitudinalaxis after each revolution of the workpiece.
 8. The method of claim 1wherein each tapered aperture includes a conical top portion.
 9. Themethod of claim 1 wherein each aperture is surrounded by a cluster ofsix peaks and six valleys.
 10. The method of claim 1 wherein the centerline to center line spacing of adjacent apertures is less than the majordiameter of the conical top portion of each adjacent aperture.
 11. Themethod of claim 1 wherein said array of peaks and valleys surroundingthe pattern of tapered apertures is configured to provide a supportmember to produce a tricot nonwoven fabric.